Son of Richard Greytail, Sly is also the first cousin of Redford Firefox. Sly was always a shy and quiet todd, who would often bury himself in his schoolwork and his love, starship mechanics. His studies in school were that of engineering and forensics. Sly loves a mystery be it of a technological origin or humanimal made. Sly was not born with any special powers like his cousin Red, but he is a very intelligent inventor and detective. On board the Solarfox, he is the ship's engineer.

Sly is trained in Vulpin Martial arts, which is a fighting form that has a lot of leg and leaping techniques, as well as standard military hand to hand training. Like Foxy, Sly is also a good marksman; not as good as Foxy, though he'd never let her know that, but does have a vaster knowledge of the use of various weapons. He is currently engaged to Foxy.